The first step in the cellular action of antidiuretic hormone (ADH) in the kidney is the stimulation of cyclic AMP formation, but it is not known how cyclic AMP acts to increase the water permeability of tubular cells. Based on our previous experimental results we proposed that cyclic AMP regulates the water permeability of tubular plasma membranes through its effect on the phosphorylation of specific plasma membrane protein involved in the regulation of cell permeability. Current findings show that microtubules will also play a role in cyclic AMP action on permeability in mammalian kidney. We intend to investigate: a) Effect of exogenous and endogenous cyclic AMP on phosphorylation of plasma membranes and microtubules of tubular cells; b) The effects of cyclic AMP on polymerization of microtubules and its interaction with membranes; c) Localization of membrane phosphorylation in the cell; d) Relation between phosphorylation and water permeability; e) Membrane and microtubule protein phosphorylation in ADH-resistant urinary concentrating defects, in attempt to demonstrate the significance of membrane phosphorylation in water permeability of the distal nephron, and to elucidate the pathogenesis of these inherited or acquired diseases. Intracellular ATP will be prelabeled with P32; plasma membranes will be isolated mostly using various forms of differential and density gradient centrifugation. Membrane protein will be isolated and identified using gel electrophoresis, ionex chromatography and gel filtration.